1. Field of the Invention
The present invention relates to devices for measuring differences in the transmission of light through an eye. More particularly, the invention relates to a non-invasive device that uses shades of color and brightness of color to determine whether the eye is impaired, e.g., by cataracts.
2. Description of the Related Art
Eye examiners perform a number of tests to determine the health of an eye. Some tests gauge the eye's health and determine ailments based on the amount of light entering or, on the contrary, leaving the eye. A cataract is one eye disease that can be detected based on the amount of light entering the eye. A cataract is defined as a clouding of a lens of an eye. The clouding of the lens blocks light entry into the eye. The amount of light entering the eye and reaching the retina is proportionally related to color perception. Hence, decreased light entry into the eye results in the eye perceiving a color as being a dark shade, while increased light entry into the eye results in the patient perceiving the color as being a light shade. Other conditions that affect light entry into the eye are thin abnormalities in the cornea or problems with the retina.
Current tests used to measure light entry into the eye measure the amount of light scattered back out of the eye, or require the use of computers. Some of these tests are invasive or are based on subjective, visual observation by an examiner, while others require the patient to perform complicated tasks. Theses tests do not measure light entry into the eye based on the patient's own ability to perceive color. Therefore, an apparatus and method is needed for measuring light entry into the eye that is non-invasive and is based on a patient's individual ability to perceive color.
U.S. Pat. No. 4,327,973, issued to Raif on May 4, 1982, describes an ophthalmoscopic instrument for measuring eye defects, such as cataracts and flares. The instrument splits a light beam into a first part and a second part. The first part is reflected off the back of the eye to a viewing station. The second part passes through a light scatterer then to the viewing station to be matched with the light of the first part. The amount of light reflected on the viewing station is quantified to determine the health of an eye.
U.S. Pat. No. 4,711,542, issued to Ichihashi et al. on Dec. 8, 1987, describes a device that photoelectrically detects the amount of backscattering resulting from a laser beam directed into the back of the eye to determine ophthalmic disease, such as cataracts. U.S. Pat. No. 5,609,159, issued to Kandel et al. on Mar. 11, 1997, describes a method and apparatus for noninvasive determination of a disease state of an eye. The test determines a patient's color mixing behavior by requiring the patient to manipulate lights of different wavelengths until a match is made. The patient's test results are then compared to a standard determined appropriate for their age group.
Several devices have been developed that test color vision in the eye by requiring a patient to discern symbols, patterns or to change a variable to match a fixed item. U.S. Pat. No. 6,379,007, issued to Farb on Apr. 30, 2002, describes an eye chart with distinct symbols and methods for vision testing. The chart displays a distinct set of numbers, letters or pictures useful in diagnosing loss of color vision and testing for neurological disorders or diseases.
German Patent Number 19,910,743 published on Sep. 14, 2000, and U.S. Pat. No. 6,220,708, issued on Apr. 24, 2001 to Koest, both describe a method and device for producing multicolored patterns to test color vision. The device transmits a time-controlled light through color segments that can be alternatively rotated into the beam of the light path.
U.S. Pat. No. 4,848,898, issued to Massof on Jul. 18, 1989, describes an apparatus for testing color vision. The device uses a mixture of yellow, red and green lights to determine color vision deficiencies, such as anomalous trichromacy and dichromacy. The lights are displayed in different patterns and light intensities.
U.S. Pat. No. 6,210,006, issued to Menozzi on Apr. 3, 2001, describes a color vision deficiency test. The test displays two separate fields, each being a different color. The first field is a fixed color such as yellow; the second field is a variable color being either green or red. The test subject is asked to determine which field corresponds to the color they are instructed to select. The test is then repeated with a different variable color. Other colors may be adjusted for other types of color deficiencies.
U.S. Pat. No. 2,462,485, issued to Freeman on Feb. 22, 1949, describes a means for testing a person's sensitivity to discriminating colors. Test plates are used having a number of chromatic spots arranged in color groups. A test subject is required to determine the number of colors that differ from the majority of colors.
U.S. Pat. No. 3,970,376, issued to Ledl on Jul. 20, 1976, describes an instrument to test color vision. The instrument comprises a number of colored glass panels that are grouped in pairs and are illuminated by a light. The glass panels include a plurality of filters to transmit light at different degrees. A test subject determines and compares the color intensity of the panels. The results tell whether or not a person is colorblind.
International Patent Number WO 99/15071, published on Apr. 1, 1999, describes a method and apparatus for testing and qualifying visual information from the eye using a virtual reality system. U.S. Pat. No. 4,169,285, issued to Walker on Sep. 25, 1979, describes a method for quantifying a person's color perception.
Other devices have been developed that test the visual acuity of the eye by testing a patient's ability to discern symbols or contrast and spatial frequency. U.S. Pat. No. 4,212,520, issued to Klimsa on Jul. 15, 1980, describes a device for testing visual acuity. The device comprises an opaque chart having a plurality of cutout openings in the shape of numbers or letters, and a contrast means disposed behind the cutouts.
U.S. Pat. No. 4,365,873, issued to Ginsburg on Dec. 28, 1982, describes a visual sensitivity test for spatial frequency and contrast sensitivity. U.S. Pat. No. 4,615,594, issued to Task on Oct. 7, 1986, describes a vision test chart. The chart displays a number of test shapes organized over a background where both the shapes and the background each have its own pre-selected luminance level. The chart tests a subject's ability to perceive contrast, specifically, contrast in relation to size.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus an apparatus and method for measuring differences in the transmission of light through a lens of an eye solving the aforementioned problems is desired.